High voltage, high power diodes are widely used in solid state horizontal CRT monitor and television deflection circuits. They provide a conduction path during a portion of the deflection cycle and damp out unwanted oscillation (see for example, Kiver and Kaufman, "Television Simplified", 7th Edition, Delmar Publishers, Albany N.Y., pages 392-398). Such devices are referred to in the art as "damper diodes", and they must be able to withstand high voltages (e g., BVR .about.400-1600 volts), carry substantial currents (e.g., IF=.about.1-10 amps), switch on and off rapidly (e.g., TRR and TFR .ltoreq.300 nanoseconds) and absorb substantial amounts of transient energy (e.g., UIS .gtoreq.1-5 milliJoules).
There is an ongoing need for greater picture definition, i.e., higher resolution, and larger screen formats in both CRT monitors and television displays. This in turn requires damper diodes with higher blocking voltages, faster switching and greater energy absorption capability. Other characteristics such as the transient forward voltage overshoot and the die size are also important.
While the properties of prior art damper diodes are adequate for some applications, they leave much to be desired for high performance applications, especially with larger format and higher resolution systems that are now emerging. Accordingly, there is an ongoing need for damper diodes having improved performance.
Various ways have been tried in the past to improve damper diode performance. For example, diode reverse blocking voltage (i.e., abbreviated BVR) and transient breakdown energy handling capability (measured as the amount of Unclamped Inductive Switching energy which a reverse biased unit can tolerate, abbreviated UIS) can be increased by increasing the resistivity and/or the thickness of the semiconductor diode depletion region. However, such modification typically increases the turn-on switching speed (i.e Transient Forward Recovery, abbreviated TFR) and the transient forward turn-on peak overshoot voltage (abbreviated TOPO).
The reverse recovery time (i.e. Transient Reverse Recovery, abbreviated TRR) may be lowered by introducing lifetime killer impurities into the space charge region. While this is successful, it increases the forward voltage drop (VF). The forward voltage drop (VF) and TOPO may be reduced and the rated forward current (abbreviated IF) may be increased by increasing the diode area (abbreviated (DA). However, larger DA results in increased device cost, which is undesirable, especially in devices intended, among other things, for consumer applications.
What is needed is a means for decreasing TFR and TOPO and increasing UIS and BVR, without increasing DA, and without significant adverse affect on TRR, IF and VF. Up to now it has not been possible to provide high voltage, high current diodes in which some or all of those properties (e.g., BVR, TFR, TRR, UIS, TOPO, etc.) most critical for more advanced CRT deflection circuits are improved without an adverse affect on other important diode parameters and/or a substantial increase in DA and cost. Accordingly, a need continues to exist for improved means and methods that overcome these deficiencies of the prior art, and especially improved means and methods for damper diodes having equal or better BVR, UIS, TFR, TRR and TOPO.